Biology of Reproduction Summers |
Endocrinology Homeostasis/Feedback Adult Female Steroid Production Ovulation |
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Adult Male Gonadal Axis Regulation Sexual Differentiation Sexual Behavior Puberty |
Reproductive Cycling Estrous Cycles Menstrual Cycle Menopause Fertilization |
Fertilization Systems Gamete Interaction Pregnancy Labor and Parturition Lactation |
Sexual Response & Behavior Pheromones STDs text: Human Reproductive Biology4th Edition- RE Jones & KH Lopez,: pp 235 - 241 Acronyms/Abbreviations end |
XXVI. Sexual Response and Behavior A. requires integration of multi-sensory input 1. balanced sensory and physiological coordination a. \ integration of neural control and endocrine modulation i. seasonal cues (e.g. light and/or To) via sensory receptors must activate HPG axis ® follicular growth and spermatogenesis (1) or puberty (2) pulsatile GnRH & LH secretion required ii. +feedback is necessary for cyclicity iii. appropriate cycle phase means appropriate Ý in hormone iv. Ý hormone (may be) required to prime neural centers for sensory information for arousal and/or behavior v. signal stimuli are sensory information which can now activate complete circuits for arousal vi. sense mediated arousal must be coordinated with sensory behavioral information vii. efferent signals stimulate endocrine and motor outputs for behavior viii. behavioral elements (there may be many) and arousal must be coordinated for successful sexual response between male and female b. many components of sexual behavior and responsivity are still unknown i. e.g. the role of hormones in human female sexual desire is controversial B. Lordosis (an example) 1. Reflex - stimulated by tactile sensory input of male body against females rump (rats) a. this reflex requires input from the brain i. input from the brain is dependent on hormone priming and sensory stimulation of arousal 2. afferent information in fibers of anterolateral spinal columns a. to 3 sites: i. lateral vestibular nucleus (LVN): postural control ii. medullary and midbrain reticular formations + midbrain central gray (1) midbrain central gray: integrates autonomic, limbic, sensory & motor information (2) midbrain reticular formation: brain arousal (3) medullary (+ pontine) reticular formations: modulation of muscular reflexes 3. E2 primes neurons of the ventromedial hypothalamus, raising the level of tonic activity a. Ý axon terminal levels of GnRH, and up-regulates P-R b. GnRH potentiates neurons of the midbrain central gray i. threshold facilitation necessary 4. E2 is followed by a short burst of P prior to lordosis (luteinization precedes ovulation) a. P: fast response - intracellular and membrane receptors b. P inhibits 5-HT i. via GABAA ii. 5-HT tonically inhibits behavior: \ P disinhibits system 5. accessory olfactory (vomeronasal) information potentiates E2/P effects a. olfactory/accessory olfactory neurons secrete GnRH i. hypothalamic GnRH develops ontogenetically from olfactory tissue b. visual input, e.g. presence of the male, also facilitates response 6. midbrain reticular formation (reflexive arousal) + midbrain central gray (hormonal + neuromodulator potentiation) neurons activate medullary reticular neurons 7. Reflex can now be completed via medullary reticular formation a. project through reticulospinal tract to ventral horn motor neurons 8. Efferent spinal neurons stimulate contraction of back muscles a. facilitated by LVN neurons C. Endocrine roles in sexual responsiveness and behavior 1. steroid hormones primarily influence sexuality of males and females by affecting sexual desire a. in some animals, e.g. rodents, steroids may influence both the ability to engage in sex and sexual interest i. in nonprimate mammals orchidectomy completely abolishes sexual behavior (1) restored by exogenous hormone ii. encephalization of sexual behavior hypothesis (Frank Beach) (1) as neocortex becomes elaborated hormones have less influence on sexual behavior (2) cortical mechanisms substitute for hormonally regulated reflexive stereotypical behavior (a) increased flexiblity and lability of sexual motivation and behavior (b) cortical mechanisms are modulated by hormones and neurogenic steroids and peptides (i) GnRH, AVP/AVT, DHEA, E2 are made centrally 2. hormonal effects on sexual behavior are influenced strongly by social context a. under some circumstances hormone levels will accurately predict the occurrence of sexual behavior i. in different social contexts the same hormonal conditions will appear unrelated to the occurrence of sexual activity ii. e.g. ovarian cycle and hormones are more important for sexual activity in multifemale groups than male-female pairs (1) female primates in pairs mate at any time; even without ovaries (2) grouped females show greatest sexual behavior midcycle; no behavior at all during early follicular or luteal phases (a) female initiation behavior = proceptivity posively correlates with [E2], negatively with [P] (b) human females exhibit Ý libido midcycle & pre- and/or post-menstrually; peak coital rate on the day of greatest [E2] and LH surge (c) adrenal androgens may be the most potent stimulators of human female sexual motivation (i) further uncoupling sexual desire and activity from cyclicity (ii) adrenalectomy eliminates sexual interest (iii) adx + aromatizable androgen replacement restores libido; menopausal women experience an Ý in sexual desire (iv) necessity of aromatization suggests E-R iii. testicular steroids are more important sexual responsivity in mulitmale-multifemale groups than male-female pairs iv. erotic arousal stimulates LH + T secretion in men (1) T decreases with age, but not in sexually active men 3. hormones are not strict regulators of sexual behavior a. castrated male humans acheive penile erection in response to sexual stimulation i. excess androgen does not produce excessive sex drive b. regulate some physical aspects of sexual functioning i. vaginal lubrication ii. rigidity of erection D. Erection - hemotumescence (another example) 1. vasocongestion leading to hemotumescence ® arterial flow into tissue > veinous drainage 2. male and female 3. spinal cord reflex a. erection reflex center in the sacral spinal cord i. erotic neural input may be direct or indirect via the brain ii. sympathetic/parasympathetic (1) innervate arterioles to corpus cavernosum, corpus spongiosum, labia minora b. erotic stimuli ® Ý parasympathetic action i. release ACh (1) ACh colocalized with VIP (2) VIP also released (a) VIP Ý ACh secretion and effectiveness (b) histamine, 5-HT, substance P, adenosine, and ATP may also mediate erection ii. sympathetic (= fight or flight) can block arousal c. ACh binds to muscarinic receptors i. M1,3,5-R activate PLC (phospholipase C) ® Ý IP3 (inositol triphosphate) ® opens endoplasmic and membrane Ca++ channels ii. Ca++ activates NOS (nitric oxide synthase) iii. NOS converts Arg to Cit; giving off NO iv. NO diffuses to all nearby cells (smooth muscle cells) v. NO binds to the heme in GC (guanylate cyclase) (1) GC ® Ý cGMP ® relax arteriole smooth muscle (a) by ¯ Ca++, dephosphorylating myosin, or Ý K+ ® hyperpolarizing cell (b) sildenafil citrate (viagra) potentiates erection by inhibiting PDE5 (phosphodiesterase5); PDE5 catabolizes cGMP d. \ NO ® arterioles dilate ® vasocongestion e. T, DHT enhance penile sensory feedback i. DHT (not aromatizable to E2) can restore penile function in castrates without reinstating male sexual behavior (1) castration eliminates erection and behavior in rats, only reduces them in primates (including humans) (a) transection of the dorsal nerve of the penis eliminates erection and intromission in rats, but not in primates (2) complete penile sensory feedback is necessary for/enhances erection, intromission, ejaculation (a) rats without senory feedback (e.g. anesthesia) mount without completing intromission and ejaculation ii. aromatizable androgens enhance sexual behavior (rats, some primates) (1) T ® Ý both penile function and sexual behavior (2) in rats aromatization blockers can eliminate sexual behavior (3) context (read neuromodulation) strongly affects the role of androgens (a) testicular suppression results in ¯ sexual behavior fast (1 wk in rhesus monkeys) in multimale groups, slower (7 wks) male-female pairs (b) A-R blockers ¯ sexual desire and interest in human males, but do not effect erections in response to sexually explicit material E. Phases of sexual response in humans 1. excitement a. female i. vaginal lubrication (10-30 s) ii. vaginal barrel Ý in length & width (inner 2/3) iii. uterus/cervix ascends (tenting) also Ý length of vagina iv. vasocongestion of clitoris, vagina, uterus, labia minora, nipples v. tumescence of clitoris (corpus cavernosum and glans), labia minora, nipples, and breasts (by 25%) vi. retraction of labia majora vii. uterine contractile fibrilliation viii. darkening of vagina, areola; sex flush or reddening abdomen, throat, chest, face, shoulders, arms, thighs (74%) ix. myotonia b. male i. vasocongestion ® tumescence of the penis (1) corpus cavernosum and corpus spongiosum ii. urethral meatus widens iii. cremaster muscle contraction elevates testes iv. scrotal skin becomes congested/thick; nipples erect (60%) v. sex flush (50-60%) vi. Ý HR, BP, breathing vii. myotonia 2. plateau a. female i. orgasmic platform = imminent orgasm: engorgment of outer 1/3 of vaginal wall, labia minora ® vaginal cavity reduced, labia become larger ii. clitoris retracts (¯ length 50%), covered by clitoral foreskin or hood iii. Ý HR, BP, breathing iv. Ý uterine fibrillation and tenting, nipple erection, breast size (maximal), darkening areola, sex flush & myotonia b. male i. slight Ý in glans of the penis, darkens, coronal ridge swells ii. urethral bulb Ý 3X iii. 1st stage of ejaculation (1) few drops from bulbourethral gland (a) may contain some sperm iv. Ý HR, BP, breathing, myotonia, sex flush, testes elevation - which rotate slightly and Ý in volume (50%) 3. orgasmic a. female i. strong muscular contractions of outer 1/3 vaginal barrel (1) 1st contraction 2-4 s (2) followed by rhythmic contractions at 0.8 s intervals (a) same frequency as male ejaculatory contractions (i) 3 -15 contractions typically (ii) status orgasmus - sustained orgasm for up to 1 min ii. expansion of inner 2/3 of the vaginal barrel iii. Oxy stimulates uterine contractions (1) ejaculation - a small amount of fluid mostly from lesser vestibular (Skene's) gland into the vestibule (2) cervical os dips iv. release of neuromuscular tension b. male i. loss of neuromuscular tension and voluntary control ii. ejaculation (1) ejaculation reflex (a) spinal cord ejaculatory center (above erection center) (i) sympathetic neural stimulation to muscles at the base of the penis (2) 2 phases (a) emmission stage: OXY + PGF2a ® sequential contraction of smooth muscle of walls of testes, epididymis, vas deferens, seminal vesicles, prostate, bulbourethral gland, ejaculatory duct; and simultaneously bladder sphincter (b) expulsion stage: rhythmic contractions of bulbocavernous muscle at the base of the penis ® expulsion of semen 4. resolution a. female i. no refractory period (1) may return to plateau ii. rapid return to normal: ceasation of vaginal contractions, clitoris leaves retracted position, ¯ HR, BP, respiration, lightening of labia minora ii. cervical os dilates immediately iii. slower: decreased muscle tension, breast & uterine size, vasocongestion of clitoris, vagina and labia minora, labia majora return to normal position b. male i. erection center sympathetically dominated (1) constricted arterioles (a) loss of tumescence ii. rapid: ¯ penis size (50%), HR, BP, respiration, muscle tension, sex flush iii. slower: final ¯ penis size, loss of nipple erection, testes/scrotal descent